Studies of murine antibody gene organization have shown that the heavy chain variable region (VH) is composed of several gene families. The usage of these gene families appears to be random in adult mice by Northern analysis of B cell hybridomas and transformed cell lines. Mice that carry the xid gene defect have been shown to be unresponsive to many polysaccharide antigens. We have examined the VH gene usage in xid versus normal mice by colony hybridization technique in order to determine whether the unresponsiveness in xid mice could be attributed to abnormal usage of the VH gene families. Splenocytes derived from CBA/Ca females (genotypically normal), CBA/N males (xid) and females (xid), and CBA/N x CBA/Ca)Fl males (xid) and females (phenotypically normal) were polyclonally stimulated and allowed to form B cell colonies on filter paper disks before hybridized with VH gene probes that define 9 different VH gene families. Our results indicate that VH gene family expression in CBA/N males and Fl males is similar to that of CBA/CA and Fl females with predominant expression of J558, the largest gene family, in all individuals. Interestingly, CBA/N female mice, which carry two defective X chromosomes, as a group expressed significantly reduced levels of the J558 gene family, and as individuals showed variation in which gene family was predominantly expressed. We conclude that the unresponsiveness of mice with the xid defect to polysaccharide antigens cannot be attributed to a failure to express the nine VH gene families that we examined. Studies are in progress to examine the expression of VH gene families in another strain of xid mice that have a BALB/c background as well as in neonatal xid and normal mice. Preliminary results indicate that the expression of VH gene families in the neonatal CBA/N is biased. The extent to which these defects relate to the inability of the CBA/N mouse to mount an antibody response to polysaccharide antigens remains to be determined.